1. Field of the Invention
This invention relates in general to antennas, and, in particular, to a multiband antenna array using radio frequency (RF) micro-electro-mechanical (MEM) switches.
2. Description of Related Art
Communications satellites are in widespread use. The communications satellites are used to deliver television and communications signals around the earth for public, private, and military uses.
The primary design constraints for communications satellites are antenna beam coverage and radiated Radio Frequency (RF) power. These two design constraints are typically thought of to be paramount in the satellite design because they determine which customers on the earth will be able to receive satellite communications service. Further, the satellite weight becomes a factor, because launch vehicles are limited as to how much weight can be placed into orbit.
Many satellites operate over fixed coverage regions and employ polarization techniques, e.g., horizontal and vertical polarized signals, to increase the number of signals that the satellite can transmit and receive. These polarization techniques use overlapping reflectors where the reflector surfaces are independently shaped to produce substantially congruent coverage regions for the polarized signals. This approach is limited because the coverage regions are fixed and cannot be changed on-orbit, and the cross-polarization isolation for wider coverage regions is limited to the point that many satellite signal transmission requirements cannot increase their coverage regions.
Many satellite systems would be more efficient if they contained antennas with high directivity of the antenna beam and had the ability to have the coverage region be electronically configured on-orbit to different desired beam patterns and/or frequency bands. These objectives are typically met using a phased array antenna system. However, phased array antennas carry with them the problems of being restricted to a single frequency band, as well as being limited by large efficiency losses.
If multiple frequency bands are to be used by the satellite for communications, the typical approach is to use two antennas with two reflectors, one antenna and one reflector for the first frequency band and a separate antenna and reflector for the second frequency band. This approach adds significant weight and size to the satellite, which limits the launch vehicle choices, and, typically, limits the size of the reflector that can be used for the frequency bands of interest. As such, smaller service areas result from the reduced size of the antenna system.
There is therefore a need in the art for a phased array antenna system that can use multiple frequency bands. There is also a need in the art for a phased array antenna system that has low efficiency losses. There is also a need in the art for an antenna system that can use multiple frequency bands and still cover a large service area.